A comparative assessment of external and internal thermal insulation for an intermittently air-conditioned building was performed numerically. The energy consumed for cooling was used to evaluate the exterior wall thermal insulation configurations. This study examined the effect of the building occupancy, the air conditioner operation mode, and the lumped indoor heat gain. The results showed that the external thermal insulation configuration provides better thermal performance than the internal insulation configuration when the building was occupied during the day. When the building was occupied during the night, the internal thermal insulation configuration showed better thermal performance if the air conditioner runs continuously during occupied hours. When the air conditioner runs intermittently by applying building thermal storage, the suitable thermal insulation configuration depended on the lumped indoor heat gain. The determination of the exterior wall insulation configuration should consider three factors: the building occupancy, the air conditioner operation mode, and the lumped indoor heat gain.
